Apparatus for radio frequency transformer control of electrical energy



April 2, 1958 J. G. D. MANWARING 2,831,953

APPARATUS FOR RADIO FREQUENCY TRANSFORMER CONTROL OF ELECTRICAL ENERGY 2Sheets-Sheet 1 Filed Feb. 10, 1955 w o V :QI M 2 ATTORNEY p l 1958 J. G.D. MANWARING 2,831,953

APPARATUS FOR RADIO FREQUENCYTRANSFORMER CONTROL OF ELECTRICAL ENERGYFiled Feb. 10, 1955 2 Sheets-Sheet 2 n t 8 S La.

(l/ll/ /'/////l (D INVENTOR. Jwfla BY KTTorNEY high-voltage insulation.

United States Patent APPARATUS FOR RADIO FREQUENCY TRANS- FORMER CONTROLOF ELECTRICAL ENERGY.

Joshua G; D. Manwaring, Medfield, Mass. Application February 10, 1955,Serial No. 487,344

4 Claims. 01. 219-1055 This invention relates to methods and apparatusfor controlling electrical energy by means of transformers and, moreparticularly, this invention is concerned with improvements in radiofrequency transformers, including those employed in induction heating,radio transmitting and various other commercial applications.

In conventional induction heating methods and apparatus, there exists aproblem of long standing. This problem arises in connection withattempts to furnish a maximum of energy transfer in a transformer whichnecessarily involves providing for a relatively high fiux linkage and,at the same time, providing for adequate These requirements, in manycases, are not satisfactorily met in conventional devices. For example,in one type of transformer mostcommonly employed, a transformer primaryis comprised by a tubular copper conductor formed into coils. One end ofthe conductor is at high potential, being connected to an R. F.high-voltage power supply; the other end is at ground potential. Aroundthe outside of-these coils is arranged a secondary consisting of a splitcylindrical copper sleeve. A' work coil is connected to and supported oneither side of the split in the .secondary in a substantially centrallylocated position and, within definite coupling limits, supplies highamperage 'low voltage output for induction heating. 7

In such a structure, increased coupling can, of course, be achieved bywrapping 'the secondary tightly around the primary coils, but this isimpractical because of the materially greater insulation problem inducedand increased coupling in this way is not feasible. Either anappreciable air insulation spacing by itself or a very small airspacingwith the use of solid insulation on the primary must be utilized.However,,even with both an air spacing and the use of solid insulationon the primary, there is not achieved sufiicient protection to avoid arelatively rapid deterioration of the solid insulation material. Thus,neither maximum coupling nor satisfactory insulation is accomplished toa degree which meets many commercial requirements.

From extensive study of the foregoing considerations and the problemindicated, there evolved the several objectives of the present inventionwhich include the object of generally providing improved methods andmeans for coupling electrical energy, as well as the more specificobjectives of dealing with the conbined coupling and insulation problemindicated in connection with induction heating; of devising methods andmeans for increasing transformer coupling and improving efficiency; ofreducing voltage insulation problems; and of developing greater primarycoil stability in transformer type energy transfer.

As a starting point in' attempting to achieve these objectives, it wasfirst conceived that a method might be devised to reduce insulationdifiiculties without coupling reduction taking place and, possibly, withcoupling being increased. In an effort to reduce insulation difliculty,there "was devised a split disc type secondary element of very 0 withthe secondary located at or very near to the ground potential or lowvoltage end of the primary coil, zero potential existed between theprimary and secondary and, therefore, a zero spacing of secondary toprimary could be employed at such a point. However,.couplingin this Iwas materially decreased.

It was then conceived that the basic idea of decreasing insulation needand simultaneously increasing coupling might be further implemented byutilizing the disc type secondary of short axial length at a zeropotential point for at least one of two associated primary coils whoserespective magnetic flux might, in some way, be controlled to producestronger inductive effects. I

In thus attempting to employ a disc type secondary of short axial lengthwith two primary coils, there was first tried an arrangement wherebyhigh potential, for example 5,000 volts, was applied to each of twoprimary coils. The flux of the two coils were developed separately butin close proximity to one another with the high potential side of onecoil being very near to the low potential side of member coil. The discsecondary was located approximately around those points at whichthe'first of the two coils was at ground potential. 4

It'was found that the two primary coils could be controlled so thatinstead of producing, as would be expected, two separate flux patterns,each of which patterns would have a region of maximum intensity in thecenter of each 'coil section, there was produced actually a combined oroverlapping pattern of flux furnished from each pri- ,mary coil so thatthe flux of each coil were, in a considerable degree, made additive toone another. However, the region of overlapping pattern of flux, it wasfound, tended to become centralized approximately around those points atwhich the first primary coil was at minimum potential but the secondprimary coil was at maximum potential. Since the disc secondary, whenplaced in position around the first coil, as near as possible to pointof zero potential, was necessarily located very close to the second coilat points of high potential, there was still an insulation problem. p

. It was further conceived at this time that it might be possible tojoin the two coils together with high potential being applied at outerends of the respective coils but with each coil connected so as to havea common center ground. In this way, the centrally located discsecondary might then realize decreased need for insulation at zeropotential point of each coil and, yet, utilizing increased flux strengthfrom both coils. This arrangement was attempted unsuccessfully with oneconthe split disc located at a point very close to the common centralground. The reason for lack of success was due to the fact that thecoils were disposed in bucking relationship and their magnetic fieldscancelled out.

It was then discovered that, by winding two coil components at two sidesof the disc secondary in such a manner that each coil extended away fromthe secondary from a common central ground and in the same direction ofturning in each instance so as to comprise mirror images of one another,the coils would no longer be bucking and there could successfully beachieved a striking increase in coupling at relatively low potential and3 with insulation difficulties being held to a minimum. This d1scoveryconstituted a very essential part of the present invention.

From this discovery, it was thereafter conceived that this strongercoupling effect might be still further augmented by selectivelycontrolling the shape and location of the primary coils with respect tothe secondary. This last concept, it was found, could be successfullyembodied by employing two primary coils of the mirror image typedescribed; enclosing the coils at their common ground point with a disctype secondary; and forming each coil component in a spiralling ordished conformation in order to bring the constituent turns of eachcomponent in close proximity to the secondary at opposite sides thereofand, preferably, in a manner such that the axial spacing of each primaryturn from adjacent secondary disc surface varies proportionately withchange in triadial spacing of said turns from the axis of the secondaryIn its broadest aspect, therefore, my invention is based on thediscovery that I may provide for an unusual and surprisingly largeincrease in coupling of magnetic flux by passing R. F. high-voltageimpulses along two primary mirror image type coils which are joinedtogether at a common ground point and which are centrally enclosed by asplit disc type secondary of short axial length and, preferably, a discwhose spacing from constituent turns of each of the coils increasesproportionately with increase in radial spacing of the turns from thecentral axis of the secondary disc. i i

The nature of the invention may be more fully understood and appreciatedfrom the following detailed description of a preferred embodimentselected for purposes of illustration and shown in the accompanyingdrawings, in which Fig. 1 is a plan view of the transformer apparatus ofthe invention shown independently of electrical circuitry and coolantconnections;

Fig. 2 is a cross-section taken on the line 2-2 of Fig. l; and

Fig. 3 is another cross-section taken on the line 3-3 of Fig. 1.

Referring more in detail to the transformer structure shown in thedrawings, I have, in general, illustrated an arrangement of disc typesecondary element of short axial length and two mirror image typeprimary coils located at either side of the secondary disc to comprisean induction heater structure of commercially acceptable nature.

Numerals 2 and 2' indicate the two primary coil components whose outerends are connected by a conductor 2a. Numeral 4 indicates the secondarydisc element. This secondary disc element 4 consists of a split annularbody of short axial length and formed from a low resistance materialsuch as copper. The split ends of the annular body 4 are provided withelectrical output members 6 and 8. These members 6 and 8 have supportedtherethrough two sections of a high current type work coil member 10,which sections are made up of tubular copper conductor portions whoseends are detachably connected by threaded couplings to respectivetubular extremities 12 and 12 of a coolant conduit 12. This conduitmember is secured to the secondary 4 and extends around its outerperipheral edge, as shown in Fig. l. A coolant, such as water, issupplied and removed through the connecting ends 14 and 16 which are, intum, connected to a suitable supply source.

The primary coil components 2 and 2 may, for example, consist of acontinuous length of copper tubing which is folded or bent over uponitself to provide a common junction or meeting point 20, as shown inFigs. 1 and 2. The two components are arranged in the form of two dishedor axially displaced spiralling coils so that the turns of each coilproject outwardly from either side of the secondary 4 and extend in the.4 same direction to thus constitute mirror images of one another.

The two outer ends of the coils are connected to a source of R. F. powerof relatively high potential, such as 5,000 volts, and each coil isgrounded at a common ground point through a ground strap 18 attached tothe junction 20. Power is delivered to the coils as R. F. high-voltageimpulses which are conducted along the surface of these tubular coils. Acoolant, such as water, is circulated through the coils from a suitablesupply source which may be taken from the same source of supply forcooling the secondary member. Each turn of the primary coils is coveredwith a solid type insulation material which provides limited insulationwith optimum induction effects and, in addition, each of the primaryturns are supported upon spacing wedges 22 located at several pointsaround the two opposite surfaces of the secondary disc 4, as best shownin Figs. 2 and 3. These wedging members thus control the degree of axialdisplacement of the respective primary coils from adjacent secondarysurfaces and thus provide a convenient means of decreasing the spacingof the primary coils with decreasing voltage potential which ranges froma maximum at the outer peripheral edges of the secondary to a minimum atthe inner peripheral edges thereof.

The structure described is characterized by several important and novelfeatures all of which combine to produce relatively heavy currentcarrying capacity with small loss. The principal feature to be noted isthat the secondary in the particular position in which it is arrangedrelative to the primary is adapted to produce a very strong coupling ofmagnetic flux. This is because the secondary occurs in the center of theprimary in the first instance and, in the second instance, thearrangement is such that much less voltage insulation is required toavoid trouble. By bringing the primary very close to the secondary, asis achieved by having two sets of spiralling coils at either side of thesecondary, a maximum of coupling is achieved at all points with theadequate amount of voltage insulation being provided for. However, it ispointed out that there is a voltage condition which is at its maximum inentering the primary where the spacing of the dish spiralling coils isgreatest and the voltage tapers to a minimum where the spacing of thetwo sets of coils is at a minimum or nearly zero magnitude.

In typical forms of the apparatus of the invention, measurements havebeen made of the Q or figure of merit of the transformer coils, i. e.,the ratio at any frequency of actual inductive reactance of the coils tothe actual resistance at that frequency. These measurements have shownmaterially increased values of Q over those of conventional transformerarrangements of comparable nature. It was found, for instance, that, ifthe flux from a conventional coil of ten turns on a two-inch diameterwas represented by the figure 10, to obtain a similar flux by my method,two coil sections of six turns each would be needed with the fluxadditive to each other and the R. F. voltage being fed into the ends andtaken out of the center. This meant that, for the same amount of fluxand a coil of approximately the same size and shape, with my method, theD. C. ohmic resistance was approximately one-quarter of the conventionalcoil and, as a result, Q, or quality factor, was increased by a multipleof four.

Another extremely important feature in the construction described is thefreedom from loss of stability in the coils in the presence of greatlyincreased coupling of the magnetic flux. By grounding the primary in itscenter loop portion and by providing for the spiralling coils extendingin the same direction away from a common groundpoint, there is achieved,to a large extent, elimination of parasitic oscillations and excessiveheating of the secondary. It will be observed that the leads on bothsides of these primary coils which are mirror images of each other areconnected together and are taken 05 in the same direction which leads toperfect symmetry, and this is of great importance in H. F. work whereeven short inductances are of great consideration.

In typical applications of induction heating utilizing the abovedescribed method and apparatus, very striking results may be obtained asis evidenced by the following examples.

Example 1 Titanium in the form of a' Ai-inch diameter rod was requiredto be heated to a temperature of 3450 F. Employing the induction heaterof the invention, the rod of titanium was brought to the indicatedtemperature in /2 second with a power available of 5 kilowatts. So faras is known, there is no commercial apparatus available for formingsuchan operation.

Example II in one commercial manufacturing process, it was required tocontinuously harden small saw blade elements by bringing these blades toa hardening temperature of 1600 F. as rapidly as possible. Employing themethod and apparatus of the invention, these saw blades were hardened ata temperature of 1600 F. and at a rate of 60 feet per minute of stock.The best performance observed by conventional equipment employed forthis purpose was heating to 1600 F. at the rate'of 17 feet per minute.

Example III In a required commercial operation, it was necessary to heatat rapid rate silvered copper wire, #20. Applicants apparatus providednecessary heating to a temperature of 1000 F. at a rate of 22 feet perminute (5 kilowatts). No comparable heating by prior art devices isknown.

Example IV understood that the invention is not limited in itsapplication or in its form of construction and the method and apparatusmay be modified and practiced in various ways. For example, theinvention, as a transformer, may be used as a coupling device for radiobroadcasting with improved efficiency to transfer energy from oscillatorto transmission line, from one transformer line to another transformerline of different characteristics, in a trans former line to radiatingelements for other antennas. Also, the primary and secondary elementsmay be desired to be used as a step-down transformer, in which case thesecondary disc becomes the primary.

Thus, from the foregoing description, it will be seen that I haveprovided an important and novel method and to the secondary electricalconductor and extending away 1" m the common ground point in the samedirection whereby high voltage impulses applied to the primary willproduce flux paths for the two coils, which flux paths combine in seriesand are additive, and the said spacedapart coils of the primaryelectrical conductor being arranged in the form of a conical helices sothat the axial spacing of constituent turns of each of the coils fromthe adjacent secondary electrical conductor varies proportionately withchange in radial spacing of said turns from the axis of the saidsecondary electrical conductor.

2. Transformer apparatus for induction heating and comprising incombination a secondary electrical conductor, said secondary electricalconductor including a disk member having an opening located centrallytherethrough to define an annular body portion, said disk member beingsplit at one point and presenting circumferentially spacedapart ends,electrical terminal members solidly fixed to said spaced-apart ends ofthe disk member, a primary electrical conductor consisting of twospaced-apart coils supported at opposite sides of the secondaryelectrical conductor, said coils being j ined together with a commoncentral ground point and having their outer ends connected to a commonterminal, each of said coils having its turns extending away from thecommon ground point in the same direction in order to cause high voltageimpulses applied on the primary to induce llux paths around the twocoils with each flux path being in series and additive, and saidsecondary electrical conductor comprising a tubular conductor elementlocated around the outer periphery of the said disk and extendingthrough References Cited in the file of this patent UNITED STATESPATENTS 891,496 Luschka June 23, 1908 1,382,905 Gravell June 28, 19212,181,899 Kennedy Dec. 5, 1939 2,355,560 Roberds Aug. 8, 1944 2,366,290Rudd Jan. 2, 1945

